This invention relates to planar inductive components.
Traditional Approach to Planar Transformers
Planar inductive components fabricated in multi-layered fashion have been published in the MEMS literature. FIG. 1 shows in exploded view a multi-layered design for a toroidal concept 10 which is typical for the state-of-the-art. Coil windings 14 are wound about the magnetic core 11 (thin circular flat ring). Separating the coils from the core are insulating layers 12, 13. For the toroid requiring magnetic laminations, the core is formed from multiple flat rings separated by non-magnetic, insulating layers. Note that the coil windings require electrical connections between the top 15 and bottom 16 segments.
The difficulties with this approach are numerous and relate to the practicality of fabrication:
a. The number of coil turns is limited by the diameter of the ring core and the ability of the fabrication process to fabricate high aspect ratio vertical coil segments.
b. The alignment requirement to connect the top and bottom segments of the coil about the core needs to be extremely precise, given the small dimension of the conductor cross-section, in order to prevent shorts and opens.
c. The connection quality between top and bottom segments of the coil becomes a significant source of electrical resistance when considering the large number of turns that may need to be connected.
d. The possibility for an open connection at one of the coil interfaces is large and renders the component unusable.
e. Leakage flux occurs since the coil turns do not totally enclose the magnetic core.
f. In the case of the DCT transformer, the difficulty in carrying out the coil construction makes it difficult to match the primary turns.
Successful fabrication of this design would require very high precision, high aspect ratio equipment and processes with very high yield risk because only one short or one open renders the component useless. The high yield risk becomes even more impractical when considering integration with ICs and packaging.
This invention addresses planar inductive components based on a linear, thin design topology that enables greater flexibility in how the components are applied, structurally and electrically. The fabrication method is multi-layered based on a layer-by-layer construction to achieve a monolithic form. Microelectromechanical Systems (MEMS) approaches based on photolithographic patterning, etching of molds and deposition can be used. Many variations on this approach are possible and depend on whether the components are formed onto macro parts, integrated with or under Integrated Circuits, embedded in circuit boards or packaging, formed separately for pick and place applications, etc.
The inductive components are linear because their inductance varies proportionately with length. Unlike wire-wound inductive coils that occupy an appreciable volume on a circuit board due to their bulkiness, the linear devices of this invention are not required to begin and end at particular locations, are wire-like and can be meandered in the plane to fit into a designed space.
The planar topology of this invention is practical to fabricate, enabling large scale production and low cost.
The inductive components of this invention include inductors, transformers, differential current transformers (DCT), isolation transformers, chokes, filters, mixers, etc.
This invention features an elongated, planar, generally linear electrical inductive component, comprising: at least one conductor, each conductor defining a unique conductive path; a magnetic core co-linear with all conductors along the entire component length, and completely surrounding all conductors; and an insulator separating each conductor from any other conductor and from the magnetic member; wherein at any location along the length of the component, in cross section the component includes only one conductor for any conductive path.
The component may comprise a single conductor, to accomplish an inductor. The magnetic core may define a magnetic circuit comprising a gap. The conductor may define a gap along its entire length, to create two full-length top and bottom halves, to allow for differential thermal expansion. The insulator may be accomplished in part by a space, to reduce the component capacitance.
The component may comprise two conductors, to accomplish a transformer, or three conductors, to accomplish a differential current transformer. The component may comprise more than two conductors to accomplish a step up or step down transformer with a desired voltage transformation from the input or inputs to the output or outputs.
The magnetic core and all conductors may meander through a plurality of turns, to increase the component""s effective length. The meanders may be essentially parallel. The magnetic core may comprise a plurality of laminations separated by non-magnetic insulating material, each lamination completely surrounding all of the conductors.
The component may comprise two or more stacked layers of meanders, to increase the conductor and core length. The component may directly connect between two spaced components in an electrical circuit, to both accomplish a desired inductance as well as carry current between the two spaced components. The invention also features a multiple inductive component inductive circuit comprising a plurality of inductive components of the type described herein, connected in a desired series and/or parallel circuit combination, to achieve a desired inductance value or voltage conversion.
Also featured is a method of fabricating this component, comprising: fabricating two essentially identical halves, each defining one half of the component; and mechanically and magnetically coupling together the two halves, to create the component.
In another embodiment, the invention features a method of fabricating an elongated, planar, generally linear electrical inductive component by multi-layered fabrication, the component having at least one conductor, each conductor in the component defining a unique conductive path, a magnetic core co-linear with all conductors along the entire component length, and completely surrounding all conductors, and an insulator separating each conductor from any other conductor and all conductors from the magnetic core member, wherein at any location along the length of the component, in cross section the component includes only one conductor for any conductive path, the method comprising: providing a lower layer of magnetic core material; providing on top of the lower layer of magnetic core material, a bottom insulator layer; providing on top of the bottom insulator the at least one conductor; providing an insulator adjacent to the outside and top of each conductor; providing, spaced to the outside of the at least one conductor and the adjacent insulator, vertical segments of the magnetic core, in contact with the lower layer of magnetic core material; and providing over the upper insulator and in contact with the magnetic core vertical segments, an upper magnetic core material, to complete a magnetic core circuit.
Also featured is a method of fabricating an elongated, planar, generally linear electrical inductive component by multi-layered fabrication, the component having at least one conductor, each conductor in the component defining a unique conductive path, a magnetic core co-linear with all conductors along the entire component length, and completely surrounding all conductors, and an insulator separating each conductor from any other conductor and all conductors from the magnetic core, wherein at any location along the length of the component, in cross section the component includes only one conductor for any conductive path, the method comprising: fabricating two component halves, each half made by: providing a lower layer of magnetic core material; providing on top of the lower layer of magnetic core material, a bottom insulator layer; providing on top of the bottom insulator layer the at least one conductor; providing an insulator adjacent to the outside of each conductor; providing, spaced to the outside of the at least one conductor and the adjacent insulator, vertical segments of the magnetic core, in contact with the lower layer of magnetic core material; and planarizing the top surface of the construction; and then mechanically and magnetically coupling together the planarized surfaces of the two halves, to complete the component.
In another embodiment, the invention features a method of fabricating an elongated, planar, generally linear electrical inductor by multi-layered fabrication, the inductor having a single conductor, a magnetic core co-linear with the conductor along the entire component length, and completely surrounding the conductor, and an insulator separating the conductor from the magnetic core, the method comprising: fabricating two component halves, each half made by: providing a lower layer of magnetic core material; providing spaced vertical segments of the magnetic core, in contact with the lower layer of magnetic core material; providing a bottom insulator layer on top of the lower layer of magnetic core material and the spaced vertical segments; providing the conductor on top of the insulator; and planarizing the top surface of the construction; and then mechanically and magnetically coupling together the planarized surfaces of the two halves, to complete the component.
In yet another embodiment, the invention features a method of fabricating an elongated, planar, generally linear electrical inductor by multi-layered fabrication, the inductor having a single conductor, a magnetic core co-linear with the conductor along the entire component length, and completely surrounding the conductor, and an insulator separating the conductor from the magnetic core, the method comprising: providing an elongated conductive wire having an essentially circular cross-section; coating the wire with a non-magnetic insulation layer; and coating the non-magnetic insulation layer with a first layer of magnetic core material. This method may further comprise creating a plurality of laminations in the magnetic core by sequentially coating the first layer of magnetic core material with one or more laminations, each comprising a coating of non-magnetic insulating material and then a coating of magnetic core material on top of the coating of non-magnetic insulating material.